Crewed earth orbiting craft derive electrical power from on-board fuel cell power systems. Operation of these fuel cell power systems produces water which is formed by the electrochemical reaction in the fuel cells. The water which is produced by the fuel cell power system is used in the space craft for evaporative cooling of the freon coolant loop in the craft during reentry into the earth's atmosphere and is also consumed by the crew. The water is periodically discharged from the operating fuel cell power systems and stored in one or more water tanks in the craft. One problem which has surfaced in connection with the discharge and subsequent use of fuel cell product water concerns the entrainment of gaseous, undissolved hydrogen in the water. In the gravity-free, weightless environment of space in which the fuel cells operate, hydrogen gas entrained in the product water will remain entrained or dispersed in the water since there is no gravitational force causing the entrained gas to rise to the top of the storage tank on the craft from whence it could be easily vented. It has been found that up to about 25% by volume of the "water" in a storage tank is, in fact, gaseous hydrogen entrained in the water. Thus, instrumentation may indicate that the water storage tank is "full" when, in truth, it is only 75% full of water. This causes problems, one of which relates to the drinking of the gas-water mixture by the crew and an other of which relates to the inability of this type of a mixture to provide the evaporative cooling capacity of pure water. It will be readily apparent that unexpected loss of cooling capability of the craft during reentry can be dangerous.